The present invention relates to a method for changing the width of a slab which is being cast by a continuous casting machine and, more particularly, to a method in which the narrow faces of a continuous casting machine are moved so as to increase or decrease the width of the slab which is being cast by the continuous casting machine.
In the field of continuous casting, particularly continuous casting of steel, there is an increasing demand for improvement in the rate of operation, as well as in the yield of the cast product. To meet these demands, continuous casting methods have been proposed and carried out in which the width of the slab which is being cast by a continuous casting machine is changed without requiring suspension of pouring of the molten metal into the mold.
On the other hand, there is a current trend that continuous casting is directly followed by rolling. This in turn gives a rise to the demand for techniques for varying the width of the cast slab in accordance with the width of the product web to be obtained while the slab is being cast continuously. In changing the width of the slab under casting without stopping the continuous casting machine, it is quite important that the length of the transient region over which the width is varied is minimized, i.e., that the aimed width is attained without delay. This in turn requires a technique which enables a quick change of the slab width.
The continuous casting machine having a width changing function is usually conducted by means of a composite casting mold which is composed of two broad faces and two narrow faces which are movable in the longitudinal direction of the broad face. The slab width is varied by moving the narrow faces towards or away from the center of the mold by a suitable means. A quick change of slab width by this method, however, encounters various problems such as an increase in the power for driving the narrow face and generation of defect. For this reason, it has been difficult to attain a higher speed of width changing with the use of the mold of the type explained.
Typical conventional methods for changing the slab widths have been disclosed in Japanese Patent Laid-Open No. 60326/1978 and Japanese Patent Publication No. 33772/1979.
On the other hand, Japanese Patent Laid-Open No. 74354/1981 discloses a method for varying the dimensions of a strand in continuous casting while casting is proceeding, wherein, during at least a portion of the time in which the pivoting movement of the mold wall takes place, the relationship between the displacement speeds of two movement-imparting device arranged above and below the narrow face is altered, and the position of the pivot axis is displaced parallel to its initial position.
The present applicant also developed methods in which the upper and lower ends of the narrow face are moved simultaneously such as to shorten the time required for the change of the width, and has proposed these methods in Japanese Patent Application Nos. 184103/1982 and 143157/1983. These methods, however, make use of translational movement of the narrow face. The methods proposed by Japanese Patent Laid-Open No. 74354/1981 and Japanese Patent Application Nos. 184103/1982 and 143157/1983 could not appreciably shorten the time required for one full cycle of width changing operation, although these methods are effective in shortening the time till the translational movement is commenced.